Paul HittandClaude Opus 5
e5815d27e2
The last of the four privacy features Android was missing that iOS already had. The sealed history file protects a phone that is off or locked; it does nothing about the phone somebody just handed to a friend. iOS asked for Face ID; on Android anyone holding an unlocked handset read every conversation. Biometrics OR the device credential, deliberately - a phone with a PIN and no fingerprint reader should still be able to use this, the same reason iOS asks for deviceOwnerAuthentication rather than biometrics specifically. Offered only when the device can actually authenticate: a switch that turns on and then cannot show a prompt locks somebody out of their own messages with no way back. Two traps worth naming. MainActivity had to become a FragmentActivity - BiometricPrompt hosts a fragment, so on a plain ComponentActivity it silently cannot show and the callback never fires, which looks like a broken lock rather than a missing base class. And the gate wraps Root rather than drawing over it: composed underneath, the message list still renders for a frame, and a frame is all a screenshot or a shoulder needs. The lock screen deliberately says nothing - no sender, no preview, no count. A lock screen reporting "3 new messages from Dana" has given away the two facts that usually matter most. The setting states what it does NOT do. This stops someone who picks up your unlocked phone; it adds no encryption, because the vault and ratchet keys are already sealed by the keystore either way. Claiming more would be selling a screen as if it were a key. Android engine, client and app suites green. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Flamenet Messenger — Android
Nothing here is an app yet. This is the engine, and it is deliberately first.
An Android client needs the protocol implemented a third time. That third
implementation is the one that finds the places where the specification says
less than the two existing engines quietly agreed on — but only if it is
written against the spec and the published vectors rather than against a
reading of our own Swift and JavaScript. So the engine comes first, it is a
plain Kotlin/JVM library with no Android in it at all, and it is held to
engine/test/vectors/protocol-v1.json — the same file the other two engines
are checked against, read from that one location rather than copied here.
./gradlew :engine:test
No Android SDK, no emulator, no device. It runs anywhere a JVM does, which is also what lets it run in CI on Linux.
What the engine covers today
| Area | Spec | State |
|---|---|---|
| Safety numbers | §7 | Done — fingerprints and conversation ordering match the published vectors |
| Key transparency verification | §19 | Done — RFC 6962 leaf/node hashing, unbalanced split, bottom-up audit paths |
| Byte helpers | — | Unsigned comparison, constant-time equality |
What it does not cover
Listed rather than left to be discovered, because a table of green ticks with the hard parts quietly missing is worse than no table:
| Area | Spec | State |
|---|---|---|
| X25519 / Ed25519 | §3 | Not started — needs a provider that works on both JVM and Android |
| X3DH key agreement | §4 | Not started |
| Double Ratchet | §6 | Not started |
| Sealed sender | §12 | Not started |
| ML-KEM-768 hybrid | §11 | Not started |
| ML-DSA-65 identities | §20 | Not started |
| Relay client | §8 | Not started |
| The app itself | — | Not started |
Until those exist, Android is honestly marked "not started" on the website, and a conversation gets the protocol's guarantees only when both ends are iOS.
Why the vectors matter more than the code
Two implementations that agree may both be wrong in the same way, especially when one was written while reading the other. The audit-path ordering in §19 is the worked example: a top-down reading of a bottom-up path produces the correct root for every left-spine index, so it passes any test that only checks index 0. The vector file pins a right-descending index for that reason, and the Kotlin tests assert both that the published path verifies and that the same path reversed does not.
If this engine ever disagrees with the file, the interesting question is which of the three is wrong — not this one by default.